Saw and impact resistant members are utilized as security bars on windows, in jails and the like, and are also bent into the U shape of a shackle for use as part of a padlock.
Conventionally, these bars are made of steel rods which are heat treated for hardness. Heat treated steel rods have only a limited resistance to saw cutting and virtually no resistance to cutting with carbide coated saws. In addition, they may be relatively easily broken by the impact of a heavy hammer.
In U.S. Pat. No. 3,777,517, of which I am a joint inventor and the sole owner, there is disclosed a padlock shackle formed of the elongated metal core within a thin walled tube with the core having longitudinally extending shallow grooves and with the grooves filled with a matrix formed of hard carbide particles and a soft material binder. This provides greater resistance to sawing because the carbide particles cause the saw teeth to break.
Similarly, the U.S. Pat. No. 3,552,938 to Draca discloses a security bar having a grooved core completely surrounded by a soft binder material with carbide particles only in the grooves.
The invention herein relates to an improved saw and impact resistant security member which eliminates the grooved core, thereby giving substantial but not complete circumferential coverage of the core with carbide particles, without any loss in the resistance to cutting by a saw.